The present invention relates to torque limiting, or torque overload, couplings for transmitting torque and motion from a drive shaft to a tubular member, which is capable of preventing the transmission of excessive torque when such excessive torque may be detrimental to related apparatus, and which is capable of transmitting only insignificant torque and no motion when the driven mechanism becomes frozen through mechanical failure or for any other reason.
Although not exclusively limited to such applications, the torque overload coupling of the invention has particular applications as a coupling for driving a conveyor roller from a power or drive shaft. In a conveyor system, one or more rollers are generally power driven, while a plurality of supporting and guiding rollers, engaging the conveyor belt, are simply supported by appropriate support means for free rotation about their axis. In the event of a jam of the articles transported by the conveyor, damage may result to the articles on the conveyor belt, to the conveyor itself, or to the conveyor driving mechanism, if the conveyor belt is continuously power driven. It is therefore desirable that the conveyor be stopped immediately, either through manual controls, thus necessitating the presence of an operator constantly at the controls, or by means of some automatic device, in order to prevent damage to the articles on the conveyor, to the conveyor itself, or personal injury to personnel. Torque limiting slip clutches and other mechanisms may be used, but torque limiting clutches, automatic torque limiting devices and other automatic shut-off devices are rather complex and costly.
The present invention, by providing a simple torque limiting coupling for driving a conveyor roller from a power shaft, automatically prevents damage in the event of a jam or of an obstruction tending to slow down or stop the motion of the conveyor belt. The present invention also permits the provision of a plurality of drive rollers for a conveyor system capable of individually adapting their respective driving torque to load conditions and to power upsurges, and capable of accepting variations in driving speed from one power shaft to another. Furthermore, the present invention permits tailoring of the torque transmitting factor of the coupling as a function of the physical dimensions of an intermediary coupling member, and as a function of its resiliency. The present invention provides a torque overload coupling utilizing rolling forces and, when operating in a disengaged mode, does not utilize slippage of friction surfaces, or engagement and disengagement of connecting elements, as is generally the case in prior art devices. The invention further provides a simple structure consisting of a single simple intermediary coupling element, and it utilizes substantially the same inventory of parts for making torque transmitting members such as a conveyor drive roller or free-wheeling support elements such as free-wheeling conveyor rollers.